1. Field of the Invention
The invention relates to a base fabric for a pressure-sensitive adhesive tape. Particularly, the invention relates to a base fabric for a pressure-sensitive adhesive tape which is made of polyester fibers not widely used hitherto in the art and is easy to tear and capable of providing a smooth torn edge when it is torn.
2. Description of the Prior Art
Recently, pressure-sensitive adhesive tapes are widely used for binding packages. One requisite for such a pressure-sensitive adhesive tape is that the tape has an ultimate elongation of from 10 to 15% in its lengthwise direction. When the ultimate elongation is more than 15%, the resultant tape is difficult to tear. In such a case, if the tape is forcibly torn, the torn edge becomes rough.
Conventional base fabrics for a pressure-sensitive adhesive tape which have heretofore been proposed are those in which a rayon spun yarn or a polyvinyl alcohol fiber yarn is used for the warp and the weft. Both of these fabrics fulfill the above-mentioned elongation requirement.
However, the base fabric made of the former spun yarn has disadvantages in that the fabric has a wet strength as low as from 45 to 55% of the dry strength, the thickness is uneven, the surface is not flat, and the fabric has an adhesive resin deposited on its surface in an excessive amount. On the other hand, the base fabric made of the latter yarn has drawbacks in that the employed raw material is expensive, the production process of the raw yarn is complicated, and the fabric has a wet strength as low as from 70 to 80% of the dry strength.
In order to resolve these drawbacks, there is proposed, in Japanese Laid-open Patent Specification No. 50-71570, a basic fabric for a pressure-sensitive adhesive tape consisting of a polyester fabric, in which a multifilament yarn with no twist (hereinafter, referred to as a flat yarn) of not more than 40 denier is employed as the warp, a low shrinkable flat yarn of a fineness of three times or more the fineness of the warp is employed as the weft, and the weft density is not less than 7 yarns/cm. In this fabric, in order to make it easy to cut the warp yarn, the fineness of the warp yarn is limited to not more than 40 denier and, in addition, a yarn with no twist is employed as the warp. The low shrinkable flat yarn is employed as the weft to avoid the dimensional change of the resulting adhesive tape which may often occur at the time of drying the fabric for the removal of a solvent after the coating of the adhesive. However, this base fabric still has drawbacks in that the thickness is uneven, the surface is not flat, and the adhesive is liable to be deposited unevenly on the surface.
Further, in Japanese Laid-open Patent Specification No. 52-58067, here is disclosed a substrate for a pressure-sensitive adhesive tape composed of a woven fabric having a yarn of a fineness of less than 0.3 mm as the warp and a yarn of a fineness of not less than 0.3 mm as the weft. In the example of this prior art, a fabric having an ultimate elongation of 49 to 62% in the warp direction is employed as the substrate for an adhesive tape. However, the adhesive tape resulting from a fabric having such a high elongation is difficult to tear, so that the torn edge becomes undesirably rough and frayed. In addition, since the fabric has a difference in the fineness between the warp and weft, the fabric has drawbacks similar to those as above-mentioned with respect to the fabric of Japanese Laid-open Patent Specification No. 50-71570.